The invention relates to a boat hull for high-speed planing hulls, the underside of which has a profile in a longitudinal section through or, respectively, parallel to the center plane similar to the profile of an aircraft wing having curvatures, the vertex point of the longitudinal sectional profile, with reference to the bow-side endpoint of the chord of the longitudinal sectional profile, being positioned in the front half of the entire length of the chord, and wherein the stern-side endpoint of the profile is positioned at the lower endpoint of the stern or, respectively, transom below the water level.
Boat hulls of similar kind are known, for example from the DE-PS 30 22 966 or, respectively, from the FR-PS 515 361; this known boat hull, however, has several disadvantages. By the relatively strong curvature of the profile of the boat hull according to the DE-PS in the front region of the profile, the flow around the boat hull is accelerated at this place, whereby a zone of low pressure is created and the boat hull in this region is "sucked on" by the water. This is called "inverse wing effect", which occurs also in connection with the underside of an aircraft wing. By reduction of the profile curvature in the rear region of the profile, the flow speed is reduced in this region with respect to the front region of the profile, whereby a zone of high-pressure is created which presses the rear end of the profile upwardly, therefore out of the water. By these two forces, namely the downwardly directed suction force in the front part of the profile and the upwardly directed pressure force in the rear part, a trim moment by the bow is created, that is a moment around a point at a place between the points of application of the lifting force and the depression force, which moment may press the bow of the boat to down, therefore downwards, so that the boat is trimmed by the bow. This trim effect generally is a function of the shape of the profile as well as of the speed of advance flow and of the inclination angle of the profile or, respectively, of the profile chord. In case of a boat hull according to the DE-PS 30 22 966, the inclination angle of the profile for the stillstanding, unloaded boat is almost 0, so that the hitherto described effect can be understood substantially as a function of the shape of the profile and the speed of advance. The just described effect that has its reasons in the shape of the profile of the boat hull, finally is superimposed by the effect of a flow against an inclined flat plate, wherein the term "flow against an inclined flat plate" must be understood as a terminus technicus.
If a watercraft vessel increases its speed, also its bow-wave is increased. If the speed of the watercraft vessel is greater than the wave propagation speed of the bow-wave of the watercraft vessel, the boat hull incides, that means it trims by the stern; in simplified words, the ship tries to ride on its own bow-wave. As already said, the boat hull thereby trims by the stern, the inclination angle of the profile is changed and thereby also the depression force of the profile changes. Substantial parts of the boat hull are no more hit by the inclined against flow as a "profile", but as a "flat plate", whereby in the forebody a buoyancy component is created which acts against the bow-heavy trim moment. Supposing that the boat can bring sufficient power, the boat reaches a planing condition, which, however, when compared with conventional planing hulls, due to the curvature of the profile in the forebody is characterized by an increased resistance caused by an increased wetted surface as well as an increased wave resistance.
Further, within this known boat hull the suction component created by the arch of the profile in the front region of the profile, due to the horizontal in-flow, is so strong that a transition into the planing condition is indeed possible, however at the same time significantly more energy is absorbed as if, for example by a reduction of the arch of the profile and simultaneous inclination of the profile, the depression force tendencies in the region of the forebody are reduced to an extent necessary to avoid an excessive sloping or, respectively, inclination of the ship body or, respectively, boat hull at the moment at which the ship or boat begins to ride on its own bow-wave, as this is the case within the known body.
Similar problems arise within the boat hull according to the FR-PS 515 361 which has a substantial bent in the course of the longitudinal sectional profile which detrimentally influences the flow along the boat hull, which boat hull is designed as a chine hull. Further, the angle included by the chord with the water surface, is too small in order to enable optimal start of planing and energy-saving planing.
Finally, from "Naval Architecture of Planing Hulls" by Lindsay Lord, 1946, the possibility has become known to calculate the resistance of a planing boat or, respectively, of an even planing plate, wherein particularly it was referred to the planing angle. In this publication a planing angle of 2.degree. has been designated as being optimal, for an angle of more than 2.degree. the wave drag could increase and for an angle of less than 2.degree. the wetted surface could increase. This, however, holds generally for all kinds of planing boats having even planing areas, however not for planing areas having the profile of an aircraft wing.
It is a basic problem of all planing vessels to lift the stern out of the water, when being under way; this is possible either by shape-conditioned, dynamic buoyancy or, however, by auxiliary lift means, such as trim flaps, side wedges etc.
The boat hull known from the DE-PS is in particular destined for sailing yawls or sailing yachts, therefore for boats without engines and shall compensate common trimming by the stern in the range of high-speed displacement mode by a trim moment by the bow and shall thereby reduce the wave resistance part which in this phase between displacement mode and planing mode naturally is very great. Simultaneously an increase of the wave resistance by a transom which is too much submerged, shall be reduced, particularly in the said speed range. Under this point of view, namely a resistance as small as possible in the border region between displacement mode and planing mode, this known shape of a boat is technically ingenious.